1. Field of the Invention
The present invention relates to a method and device to limit or prohibit duplication of information such that, for example, an information signal recorded on a recording medium is reproduced and transmitted in the analog signal state with an information for preventing duplication, and the transmitted information signal is received and recorded on another recording medium; and an information output device to be used for the device.
2. Description of the Related Art
Video Tape Recorders (VTRs) have been widespread, and there have been provided great many software applications that VTRs can reproduce. In recent years, reproduction devices such as the digital VTR and DVD (digital video disk) have come into reality. Thereby, people are able to easily reproduce good pictures and sounds to watch and listen.
However, there has been a risk that software applications thus abundantly provided are duplicated unlimitedly, and various measures for preventing duplication have been adopted so far.
For example, there is a method for substantially preventing duplication by exploiting the difference in the AGC (auto gain control) system between a VTR as a recording device and a monitor receiver to provide pictures, or the difference in the APC (auto phase control) characteristic.
That is, the VTR applies, for example, an AGC system that employs a pseudo synchronizing signal interpolated into the video signal, and the monitor receiver applies another AGC system that does not employ the pseudo synchronizing signal. The duplication prevention method that utilizes the difference in the AGC system interpolates an extremely high level of a pseudo synchronizing signal as a synchronizing signal for the AGC when recording analog video signals on an original recording medium, and interpolates the extremely high level of a pseudo synchronizing signal into the video signals supplied to a recording VTR from a reproducing VTR as a synchronizing signal for the AGC.
And, the VTR applies an APC system that employs the phase of the color burst signal itself of the video signal, and the monitor receiver applies another APC system. The duplication prevention method that utilizes the difference in the APC characteristic partially inverts the phase of the color burst signal of the video signal, and outputs the video signal partially inverted in the phase of the color burst signal as the video signal supplied to the recording VTR from the reproducing VTR, when recording analog video signals on an original recording medium.
With the system thus arranged, the monitor receiver that receives analog video signals from the reproducing VTR is able to reproduce a normal picture without being affected by the pseudo synchronizing signal or the partial phase inversion of the color burst signal used for the APC.
However, when the VTR receives analog video signals having the pseudo synchronizing signal interpolated or the analog signals having the phase of the color burst signal partially inverted from the reproducing VTR as in the foregoing, and records the analog video signals on a recording medium, the VTR cannot properly perform the gain control, or the phase control in accordance with the input signal; thus the VTR is not able to normally record the video signals. Accordingly, the VTR cannot present a normal picture good for watching and listening when reproducing the recorded video signal.
Such a method for processing analog video signals is does not prohibit duplication, but prevents a normal reproduced picture good for watching and listening from being to be obtained, which is in a sense a passive control from preventing duplication.
On the other hand, in processing digitized data, for example, digitized video signals, a direct control for preventing duplication is adopted such that a duplication control signal made of a duplication prevention code, a generation limitation code of duplication, or the like is added on the video signal as digital data and recorded on a recording medium to thereby prohibit duplication.
FIG. 1 is a basic block diagram of a reproducing and recording system for processing digitized data. A digital information signal reproduced by a digital reproducing device 110 is transmitted to a digital recording device 120 through a digital transmission line 101. The recording device performs duplication in case the digital information signal permits duplication, and prohibits duplication in case the digital information signal does not permit duplication.
On a recording medium 111 mounted on the digital reproducing device 110, a duplication control information as an added information is recorded in addition to a main digital information. The duplication control information indicates the contents of control such as duplication prohibition, duplication permission, generation limit of duplication. A digital reproducing unit 112 reads out an information signal from the recording medium 111, and acquires the duplication control information as well as the main digital information, which are transmitted to the digital recording device 120 through the digital transmission line 101.
A duplication control signal detection unit 122 of the digital recording device 120 detects a duplication control signal from an information signal received through the digital transmission line 101, and discriminates the contents of control. And, the detection unit 122 transmits the discrimination result to a digital recording unit 121.
When the discrimination result of the duplication control signal from the duplication control signal detection unit 122 indicates permission to record the digital information through the digital transmission line 101, the digital recording unit 121 converts the foregoing inputted digital signal into a digital information suitable for recording, and writes it on a recording medium 123. On the other hand, when the discrimination result of the duplication control signal from the duplication control signal detection unit 122 indicates duplication prohibition, the digital recording unit 121 is designed not to record the foregoing input digital information.
Further, when the discrimination result of the duplication control signal from the duplication control signal detection unit 122 indicates permission to duplicate only for the first generation, the digital recording unit 121 converts the foregoing input digital signal into a digital information suitable for recording, and writes it on the recording medium 123, and at the same time, changes the duplication control signal as an added information into a signal to indicate duplication prohibition (duplication prohibition for the next generation), and records the signal on the recording medium 123. Accordingly, it becomes impossible to duplicate video signals using the duplicated recording medium 123.
Thus, in case of the so-called digital connection such that the main information signal and the duplication control signal as an added information are supplied to the recording device as a digital signal, using the duplication control signal can secure the duplication control such as duplication prohibition in the recording device.
Incidentally, if the digital reproducing device in FIG. 1 is a digital VTR, for example, in order to monitor reproduced video signals and audio signals, only the video signals and audio signals in main information signals are converted into analog signals through a D/A converter 113, which are usually supplied to a monitor receiver through an analog output terminal 114.
In this manner, although the reproducing device is for digital information, the analog signal supplied from the analog output terminal 114 does not contain the duplication control signal. Accordingly, if an analog VTR is connected to the analog output terminal 114, duplication of information signals becomes possible.
Accordingly, it is suggested to superimpose the duplication control signal on the D/A converted video signals and audio signals. However, it is difficult to superimpose the duplication control signal without deteriorating the D/A converted video signals and audio signals, and to take out the duplication control signal in the recording device to utilize it for duplication prevention control.
Therefore, in the analog connection, there has been only the passive method for preventing duplication that utilizes the difference in the AGC system between the foregoing VTR and the monitor receiver or the difference in the APC characteristic therebetween.
Incidentally, in the control method for preventing duplication that utilizes the difference in the AGC system between the foregoing VTR and the monitor receiver or the difference in the APC characteristic therebetween, there is a case that video signals can be recorded unexpectedly normally depending on the AGC system or the APC characteristic of the recording device and therefore even the passive duplication prevention cannot be carried out. Further, there has been a problem that disturbances can be generated on the reproduced picture on the monitor receiver.
In order to solve the foregoing problems, as an effective duplication control method that can be applied to either of the analog connection and the digital connection, without deteriorating reproduced picture and audio signals, the applicant has proposed a digital recording method and analog recording method of video signals in which the spectrum of a duplication control signal is spread, and the spread spectrum duplication control signal is superimposed on the video signals in the analog signal state (refer to Japanese Patent Application Laid-Open No. Hei 7-339959).
In this method, a PN (Pseudo random Noise) sequence code (hereunder, referred to as PN code) used as a spectrum spreading code is generated in a sufficiently fast rate, and the duplication control signal is multiplied by the PN code to thereby spread the spectrum of the duplication control signal. As the result, a narrow band and high level duplication control signal is transformed into a wide band and low level signal that does not affect the video signals and audio signals. And, the spread spectrum duplication control signal is superimposed on the analog video signals to be recorded on a recording medium. In this case, it is possible to record either of the analog and digital video signals on a recording medium.
In this method, since the duplication control signal is superimposed on the video signals, as a spread spectrum, wide band and low level signal, it is difficult for a person making an illegal duplication to remove the duplication control signal from the video signals containing the duplication control signal.
However, it is possible to extract the duplication control signal from the video signals containing the duplication control signal by applying a reverse spectrum spreading processing to the duplication control signal. Therefore, the duplication control signal as well as the video signals can reliably be provided to the recording device, and at the same time the duplication control signal can be extracted on the side of the recording device and the duplication control can reliably be carried out in accordance with the extracted duplication control signal.
As described above, it is difficult to remove the duplication control signal that has been transformed into a spread spectrum signal and superimposed on the video signals from the mixture of both, which, however, is theoretically possible.
For example, when the spread spectrum duplication control signal bears a constant level, a possible method receives the video signals containing the foregoing duplication control signal before supplying the video signals to the recording device, and detects the spread spectrum duplication control signal that is superimposed on the video signals. Further, the method generates a canceling signal having the same level and same phase as the spread spectrum duplication control signal superimposed on the video signals on the basis of the detected duplication control signal, and subtracts the canceling signal from the video signals on which the spread spectrum duplication control signal is superimposed. Thereby, it is possible to wipe out the spread spectrum duplication control signal superimposed on the video signals.
Thus, the duplication control signal superimposed on the video signals is removed, and accordingly, duplication of the video signals, which is prohibited, will become possible. This incurs a risk that allows the illegal duplication of video signals.
Further, when a duplication control signal as well as video signals is recorded on a recording medium, the duplication prevention control in the foregoing analog connection is difficult as described above.